Data storage capacity has grown to a point where it is now feasible to carry personal data, an operating system and applications on a single portable storage device such as a portable hard disk drive or USB flash drive device. It is possible to boot a computer system or another device to run with an operating system that is stored on such a storage device.
Most host computing devices and other devices have a BIOS or firmware that is architected such that the BIOS or firmware inspects the first sector of a disk to bootstrap the operating system. However, a disk can only have one instance of a first sector. As a result, booting multiple operating systems from a single physical disk requires a boot manager that resides in the first sector of the disk, and then continues the boot process based on user selection; this works with some personal computers, but not all, and typically not with other bootable devices. Boot managers are architecture-specific or host-specific, and thus a single physical disk cannot be used for booting devices of differing architectures, such as a game console, a PowerPC host and an x86 PC.